Bulletin of the Geological Society of Malaysia, Volume 45, May 2002, pp. 71 – 80

Kajian geokimia batuan igneus sekitar Gunung Pulai, Johor

(Geochemical study of igneous rocks around Gunung Pulai area, Johore)

Sia Chee Chuan and Mohd Rozi Umor

Program Geologi, Pusat Pengajian Sains Sekitaran dan Sumber Alam, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, . 43600 Bangi,Selangor

Abstrak: Kawasan di sekitar Gunung Pulai terdiri daripada batuan igneus dan batuan sedimen. Batuan igneus terbahagi kepada batuan plutonik dan batuan volkanik. Granit merupakan batuan igneus yang utama terdiri daripada granit biotit dan granit hornblend. Selain itu, terdapat juga granodiorit yang berbutir sederhana hingga kasar. Kajian terdahulu menunjukkan bahawa usia bagi granit ini ialah Trias hingga Kapur Awal. Batuan volkanik merupakan Ahli Volkanik Gunung Pulai dalam Formasi Jurong. Batuan volkanik terdiri daripada riolit dan piroklas. Sepuluh unsur major dan minor yang ditentukan ialah SiO₂, TiO₂, AI₂O₃, Fe₂O₃, FeO, MnO, CaO, Na₂O, K₂O dan P₂O₅. Sementara itu, 12 unsur surih terdiri daripada As, Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V, Zn dan Zr dianalisis. Hasil daripada analisis XRF, didapati bahawa purata (julat) peratus berat (wt %) unsur major dan minor bagi granitoid adalah: SiO₂ 74.77 (67.84-79.92), TiO₂ 0.18 (0.05-0.53), AI₂O₃ 13.63 (11.21-15.93), Fe₂O₃ 1.96 (0.63-4.97), MnO 0.05 (0.01-0.22), MgO 0.17 (0.02-1.06), CaO 1.54 (0.18-4.19), Na₂O 3.03 (2.56-3.58), K₂O 4.02 (2.74-4.82) dan P₂O₅ 0.03 (0.01-0.12). Manakala purata (julat) unsur surih adalah:·Ba 487 (0-744), Zr 140 (115-186), Sr 99 (40-191), Rb 206 (123-336), Pb 28 (4-83), As 18 (11-26), Zn 25 (0-91), Cu 19 (13-38), Co 17 (0-42), Ni 5 (1-7), Cr 12 (7-22) dan V 17 (2-59). Dari kajian geokimia, granitoid ini dikelaskan sebagai jenis I dengan sifat batuan peralumina. Indeks alkali kapur bagi granitoid ini ialah 64. Hasil analisis geokimia menunjukkan batuan granitoid di kawasan kajian adalah hasil dari proses pembezaan magma dengan arah pembezaan dari batuan granodiorit ke granit. Manakala bagi riolit, peratus berat (wt %) bagi unsur major dan minor yang dianalisis ialah SiO₂ 74.99, TiO₂ 0.10, AI₂O₃ 13.14, Fe₂O₃ 1.28, MnO 0.02, MgO bdl, CaO 1.31, Na₂O 2.60, K₂O 4.42 dan P₂O₅ 0.01. Sementara itu, nilai kepekatan (ppm) bagi unsur surih pula ialah Ba 595, Zr 144, Sr 96, Rb 254, Pb 24, As 17, Zn bdl, Cu 16, Co bdl, Ni 3, Cr 9 and V 6.

Abstract: The Gunung Pulai area is mainly underlain by igneous rocks and sedimentary rocks. The igneous rocks comprises plutonic and volcanic rocks. Granite is the main rock and consists of biotite granite and hornblende granite. There are also medium to coarse-grained granodiorite. The previous study showed that the age of these granites is early Triassic to early Creataceous. The volcanic rocks belong to the Gunung Pulai volcanic member of the Jurong Formation. The volcanic rocks are rhyolite and pyroclastics. The rocks were analysed for SiO₂, TiO₂, AI₂O₃, Fe₂O₃, MnO, CaO, Na₂O, K₂O and P₂O₅. The 12 trace elements analysed were As, Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V, Zn dan Zr. From XRF analysis, the average (range) for major and minor elements (wt %) are: SiO₂ 74.77 (67.84-79.92), TiO₂ 0.18 (0.05-0.53), AI₂O₃ 13.63 (11.21-15.93), Fe₂O₃ 1.96 (0.63-4.97), MnO 0.05 (0.01-0.22), MgO 0.17 (0.02-1.06), CaO 1.54 (0.18-4.19), Na₂O 3.03 (2.56-3.58), K₂O 4.02 (2.74-4.82) and P₂O₅ 0.03 (0.01-0.12). Meanwhile, the average (range) for trace elements are: Ba 487 (0-744), Zr 140 (115-186), Sr 99 (40-191), Rb 206(123-336), Pb 28 (4-83), As 18 (11-26), Zn 25 (0-91), Cu 19 (13-38), Co 17 (0-42), Ni 5 (1-7), Cr 12 (7-22) dan V 17 (2-59). From geochemical studies, the granitoid are classified as I-type and peraluminous. The calc-alkaline value for the granitoid in the area is 64. Results from geochemical analysis show that granitoid rocks in the study area result from magma evolution from granodiorite to granite. Besides that, the weight percentage (wt%) for major and minor elements of rhyolite is SiO₂ 74.99, TiO₂ 0.10, AI₂O₃ 13.14, Fe₂O₃ 1.28, MnO 0.02, MgO bdl, CaO 1.31, Na₂O 2.60, K₂O 4.42 and P₂O₅ 0.01. Meanwhile, the concentration (ppm) of trace elements is Ba 595, Zr 144, Sr 96, Rb 254, Pb 24, As 17, Zn bdl, Cu 16, Co bdl, Ni 3, Cr 9 and V 6.

https://doi.org/10.7186/bgsm45200211